Abstract
Ganoderma lucidum is a medicinal fungus whose numerous triterpenoids are its main bioactive constituents. Although hundreds of Ganoderma triterpenoids have been identified, Ganoderma triterpenoid glycosides, also named triterpenoid saponins, have been rarely found. Ganoderic acid A (GAA), a major Ganoderma triterpenoid, was synthetically cascaded to form GAA-15-O-β-glucopyranoside (GAA-15-G) by glycosyltransferase (BtGT_16345) from Bacillus thuringiensis GA A07 and subsequently biotransformed into a series of GAA glucosides by cyclodextrin glucanotransferase (Toruzyme® 3.0 L) from Thermoanaerobacter sp. The optimal reaction conditions for the second-step biotransformation of GAA-15-G were found to be 20% of maltose; pH 5; 60 °C. A series of GAA glucosides (GAA-G2, GAA-G3, and GAA-G4) could be purified with preparative high-performance liquid chromatography (HPLC) and identified by mass and nucleic magnetic resonance (NMR) spectral analysis. The major product, GAA-15-O-[α-glucopyranosyl-(1→4)-β-glucopyranoside] (GAA-G2), showed over 4554-fold higher aqueous solubility than GAA. The present study demonstrated that multiple Ganoderma triterpenoid saponins could be produced by sequential actions of BtGT_16345 and Toruzyme®, and the synthetic strategy that we proposed might be applied to many other Ganoderma triterpenoids to produce numerous novel Ganoderma triterpenoid saponins in the future.
Highlights
Ganoderma lucidum is a medicinal fungus which has been used as a dietary supplement to promote healthiness in Asia for thousands of years [1]
Some studies demonstrated that these triterpenoid saponins possess more bioactivities than the aglycon forms [7,8,9,10]
Due to the high cost of uridine diphosphate-glucose (UDP-G), some scientists focus on finding novel enzymes that use inexpensive sugar, such as starch, dextrin, maltose, or sucrose, as sugar donors to catalyze the glycosylation of small molecules [18,19,25]
Summary
Ganoderma lucidum is a medicinal fungus which has been used as a dietary supplement to promote healthiness in Asia for thousands of years [1]. Due to the high cost of UDP-G, some scientists focus on finding novel enzymes that use inexpensive sugar, such as starch, dextrin, maltose, or sucrose, as sugar donors to catalyze the glycosylation of small molecules [18,19,25]. Most of these novel enzymes belong to either glycoside-hydrolases (GH) family 13 (GH13), such as α-amylase (E.C. 3.2.2.1), α-glucosidase (E.C. 3.2.1.20), amylosucrase (E.C. 2.4.1.4), and cyclodextrin glucanotransferase (E.C. 2.4.1.19), or GH 70, such as dextransucrase (E.C. 2.4.1.5) [18,19,25]. Both the chemical structures and the aqueous solubility of the products were determined further
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